1. Field of the Invention
The present invention relates to a feedback controller controlling an output of a controlled object in accordance with a reference value.
2. Description of the Related Art
In conventional, there has been used a feedback controller controlling an output of a controlled object in accordance with a reference value.
FIG. 9 shows the basic structure of the controller for performing a feedback control.
This type of controller compares an output value eo (controlled variable) of a controlled object 10 with a control reference value R for the amount of controls supplied from an external unit, and amplifies a difference between the output value eo and the reference value R by a controller 20. Then, the controlled object 10 is operated by a manipulated variable ec in accordance with the compared and amplified result such that the controlled variable eo is controlled to be equal with the control reference value R.
Such control is called as a feedback control since the controlled variable eo is fed back to the input of the controller 20.
Unexpected disturbance D is often added to the controlled object 10 from an external source. In such a case, the variation of the controlled variable due to disturbance D is fedback to the controller 20, and the manipulated variable ec is varied. As a result, the variation of the controlled variable eo due to disturbance D is suppressed.
As a method for realizing the feedback control, an analog calculation method are performed using a calculation amplifier and a digital calculation method using a microcomputer.
The analog calculation control is called as a continuous control system since signals such as the reference value and the controlled variable to be fedback are continuously controlled. On the other hand, the digital calculation control is called as a sampled-data control since signals sampled at a certain time interval are controlled.
In the sampled-data control, there is a control method, which is called "deadbeat control". According to the deadbeat control method, the controlled variable can be set in finite time even if the reference value and disturbance are varied.
In the deadbeat control of the sampled-data control, however, since the manipulated variable ec varies stepwise, a case, which is unfavorable to the controlled object, often occurs. For example, in a case where a motor control is carried out, there is a case in which large shock is given to a machine, which is used as a load and is connected to a motor. In recent years, there has been proposed a robust control method in which a sampling cycle is shortened and the controlled variable is set at relatively many numbers of sampling to be strong against the parameter variation of the controlled object. The robust control is difficult to be realized since the controller is complicated and the number of gains, which is necessary for controlling the controller, is increased.
Published Unexamined Japanese Patent Application (PUJPA) No. 3-100801 discloses a controller for performing the similar deadbeat control in the continuous control system. In the deadbeat control of the continuous control system, there is an advantage in which the degree of deterioration is smaller than with the deadbeat control of the sampled-data control system. In the description of PUJPA No. 3-100801, if a delay element of delay time, which is the same as the time to be set is used in the controller, a response to an reference value in the continuous control system and a response to disturbance can be set in finite time.
Even if it is understood that deadbeat control will be realized in the continuous control system if the delay element of delay time, which is the same as the time to be set is used in the controller, it is difficult to obtain the structure of the controller, which can realize the deadbeat control in the continuous control system. Therefore, in the present circumstances, the specific structure of the controller is obtained by a trial-and-error method.
Due to this, it is extremely difficult to apply the controller described in PUJPA No. 3-100801 to the complicatedly structured controlled object.